Plasma membranes SAC 1 - help!

[Chromeo33]

So we're doing an experiment that involves exposing beetroot cells (and effectively plasma membranes) to 3 solutions of:
- Distilled water
- Detergent
- Vinegar

Now our teacher hasn't taught us anything on the topic..
I know that the cell's supposed to rupture and let its dye out..
But for which solutions does it do this and why?

[happyhappyland]

Read your notes, textbook on osmosis.. if theres anything you dont understand there then ask here again!

[Chromeo33]

No I dont think it had anything to do with osmosis, moreso to do with the effect of various pH levels on the plasma membrane's proteins

I'm just not sure as to how the acidity of a solution affects the plasma membrane..

[dooodyo]

Oh chromeo I just did that question lol  

It actually doesn't affect the phospholipid bilayer, infact an
acidic solution breaks down the structure of proteins by breaking
the hydrogen bonds and di-sulfide bridges. This in turn leads to
loss of functional conformation which then creates holes in the
membrane through which the pigment can leak out.

[Chromeo33]

Oh chromeo I just did that question lol 

It actually doesn't affect the phospholipid bilayer, infact an
acidic solution breaks down the structure of proteins by breaking
the hydrogen bonds and di-sulfide bridges. This in turn leads to
loss of functional conformation which then creates holes in the
membrane through which the pigment can leak out.

Sweeeet thanks for that! But you mention the effect of acidic solutions on the plasma membrane (i.e. pH values of < 7), but what would happen in the case of exposing cells to basic solutions (i.e. pH values of > 7)?

[dooodyo]

Oh it would cause them to form spherical micelles
which would just completely ruin the structural
integrity of the membrane. Thus the membrane
would completely be damaged.

[Drunk]

HOW would the acids actually break down the hydrogen bonds and how would the bases rearrange the phospholipids exactly? on like, a chemical level?

[dooodyo]

Hmm... yeah I wanted to know as well but my teacher said it was unnecessary  . I suppose its got to do with the fact that an acidic
solution has a higher concentration of hydrogen ions than in a neutral solution so that would mean perhaps these hydrogens could change the folding of the membrane proteins and so loss of structure = complete loss of the functional conformation for the protein.

In regards to the basic solution the best I could get was from the Heinemann 2 textbook which says that, " if the tails are short, the phospholipids spontaneously form a spherical micelle".    

[Chromeo33]

HOW would the acids actually break down the hydrogen bonds and how would the bases rearrange the phospholipids exactly? on like, a chemical level?

Yeah I asked my Biology teacher as to how much depth we should actually go into answering the questions, and she said that we didn't need to go into full biochemical detail as this wasn't Chemistry but Biology.

But I'm guessing it couldn't hurt to address the chemical aspect of the experiment..

[Truck]

So we're doing an experiment that involves exposing beetroot cells (and effectively plasma membranes) to 3 solutions of:
- Distilled water
- Detergent
- Vinegar

Now our teacher hasn't taught us anything on the topic..
I know that the cell's supposed to rupture and let its dye out..
But for which solutions does it do this and why?

From my notes (haven't done the SAC yet);
Distilled water should do nothing because the pH is 7 so it's neutral, and Osmosis doesn't occur... so it's the control.

Detergent disrupts the structure of the membrane because it emulsifies the phospholipids, whilst also forming micelles which tear apart the membrane.

Vinegar is acidic. Proteins will try to stabilize acidic or basic solutions by either gaining or losing H+ ions because they're amphoteric and the plasma membrane is ~70% protein. This will cause the shape of the protein to change and thus damage the membrane.

Sound about right?

[dooodyo]

Hmmm yeah sounds about right but what do you mean by
"emulsifies the bonds in the phospholipids"?

[Drunk]

Hmmm yeah sounds about right but what do you mean by
"emulsifies the bonds in the phospholipids"?

They pretty much create a coat over the phospholipids and I'm assuming the phospholipids get pulled apart by this emulsification

[Truck]

Emulsify - To make into an emulsion.
Emulsion - A suspension of small globules of one liquid in a second liquid with which the first will not mix.

Cheers for the clarification Chris!

EDIT: Soaps and detergents emulsify by surrounding small globules of fat, preventing them from settling out. Found this on http://medical-dictionary.thefreedictionary.com/emulsify. Pretty useful explanation.

[Chromeo33]

Dang, the SACs over already and I didnt include this emulsification (is that a word) stuff!

Thanks anyway peepssssss!